With the development of wireless communication technology, more and more application techniques have been developed. These application techniques employ wireless communication facilities to provide new interactive information modes for users and work in a variety of scenarios. However, the rapid emergence of these application techniques also leads to unprecedented challenges to the wireless communication technology. Among the numerous challenges, the rapidly-developing service of the Internet of Things is becoming a hot spot of wireless communication research. In order to provide a network through which a person can be seamlessly connected with nature and machines, and even through which machines can be connected seamlessly to other machines, the wireless communication technology may adopt new solutions to deal with potential demands.
The Internet of Things refers to access devices that may be extended from people to objective things. It is expected that the number of such access devices will greatly increase in the future. By 2020, the number of devices wirelessly connected may be 100 times the current number. On the other hand, most applications of the Internet of Things, such as devices for remote meter reading, environmental monitoring, and industrial control, are all restricted to limited application scenarios. As such, these devices generate a small amount of data and have a longer duty cycle. Thus, from the perspective of the communication network, a concern regarding the Internet of Things is how to efficiently support a long duty cycle of a large number of devices and small data packets sporadically sent from the devices.
To meet the demand for wireless data traffic, which has increased since the deployment of 4th-Generation (4G) communication systems, efforts have been made to develop an improved 5th-Generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post long term evolution (LTE) System’.
The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), antenna arrays, analog beam forming, and large scale antenna techniques are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like.
In the 5G system, Hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
The Internet, which is a human centered connectivity network where humans generate and consume information, is now evolving to the Internet of Things (IoT) where distributed entities, such as things, exchange and process information without human intervention. The Internet of Everything (IoE), which is a combination of the IoT technology and the Big Data processing technology through connection with a cloud server, has emerged. As technology elements, such as “sensing technology”, “wired/wireless communication and network infrastructure”, “service interface technology”, and “Security technology” have been demanded for IoT implementation, a sensor network, a Machine-to-Machine (M2M) communication, Machine Type Communication (MTC), and so forth have been recently researched. Such an IoT environment may provide intelligent Internet technology services that create a new value to human life by collecting and analyzing data generated among connected things. IoT may be applied to a variety of fields including smart home, smart building, smart city, smart car or connected cars, smart grid, health care, smart appliances and advanced medical services through convergence and combination between existing Information Technology (IT) and various industrial applications.
In line with this, various attempts have been made to apply 5G communication systems to IoT networks. For example, technologies such as a sensor network, Machine Type Communication (MTC), and Machine-to-Machine (M2M) communication may be implemented by beamforming, MIMO, and array antennas. Application of a cloud Radio Access Network (RAN) as the above-described Big Data processing technology may also be considered to be as an example of convergence between the 5G technology and the IoT technology.
In an LTE system corresponding to the Evolved Universal Terrestrial Radio Access (E-UTRA) protocol developed by the 3rd Generation Partnership Project (3GPP), uplink transmission of a mobile terminal uses a Single Carrier Frequency Division Multiple Access (SC-FDMA) modulation scheme. In order to avoid multi-user interference, uplink transmission of multiple users is performed using a synchronous transmission scheme. That is, the time of uplink signals of the multiple users reaching a base station is strictly aligned. To achieve this uplink synchronization transmission, the LTE system adopts an uplink timing advance scheme. The base station uses downlink control signaling to inform the mobile terminal of an advance value between the time of transmitting an uplink signal and the time of receiving a downlink signal. Before the base station obtains an initial timing advance value of the mobile terminal, the base station may generally consider that the mobile terminal is in an asynchronous state. The mobile terminal in the asynchronous state is not allowed to transmit uplink data so as to avoid potential interferences. The process of obtaining, by the base station, the initial timing advance value of the mobile terminal is called an uplink synchronization process.
The uplink synchronization of LTE uses a random access procedure, in which, under a contention scheme, a terminal transmits a randomly-selected physical random access channel (PRACH) preamble (which may also be referred to as a Signature). A base station detects the preamble signal, estimates the uplink reception time, and calculates a timing advance value based on the estimated uplink reception time.
FIG. 1 is a schematic diagram illustrating an LTE random access procedure according to the related art.
Referring to FIG. 1, after the random access preamble is transmitted, the random access procedure may complete subsequent steps to complete the whole random access procedure.
At operation 105, the terminal transmits the random access preamble to the base station.
At operation 110, the base station returns a random access response to the terminal.
At operation 115, the terminal transmits the message to the base station.
At operation 120, the base station transmits a contention resolution message to the terminal.
FIG. 2 is a schematic diagram illustrating a structure of an LTE PRACH preamble according to the related art.
Referring to FIG. 2, the preamble is composed of two parts including a cyclic prefix (CP) and a Sequence. The lengths of the CP and/or the Sequence of different preamble formats are different.
The preamble formats currently supported by both the time division duplexing (TDD) mode and the frequency division duplexing (FDD) mode in the LTE system are shown in Table 1.
TABLE 1Preamble formatsPreamble formatTCPTSEQ0 3168 · Ts24576 · Ts121024 · Ts24576 · Ts2 6240 · Ts2·24576 · Ts321024 · Ts2·24576 · Ts4 448 · Ts4096 · Ts(only applied to the TDD mode)
In the frequency domain, each PRACH described above occupies six physical resource blocks (PRB). Each PRB includes twelve subcarriers, and the bandwidth of each subcarrier is 15 kHz. Random access configurations of the LTE FDD system and the LTE TDD system are respectively shown in Table 2 and Table 3.
TABLE 2Random access configuration of LTE FDD systemPRACHSystemConfigurationPreambleframeSubframeIndexFormatnumbernumber00Even110Even420Even730Any140Any450Any760Any1, 670Any2, 780Any3, 890Any1, 4, 7100Any2, 5, 8110Any3, 6, 9120Any0, 2, 4, 6, 8130Any1, 3, 5, 7, 9140Any0, 1, 2, 3,4, 5, 6, 7,8, 9150Even9161Even1171Even4181Even7191Any1201Any4211Any7221Any1, 6231Any2, 7241Any3, 8251Any1, 4, 7261Any2, 5, 8271Any3, 6, 9281Any0, 2, 4, 6, 8291Any1, 3, 5, 7, 930N/AN/AN/A311Even9322Even1332Even4342Even7352Any1362Any4372Any7382Any1, 6392Any2, 7402Any3, 8412Any1, 4, 7422Any2, 5, 8432Any3, 6, 9442Any0, 2, 4, 6, 8452Any1, 3, 5, 7, 946N/AN/AN/A472Even9483Even1493Even4503Even7513Any1523Any4533Any7543Any1, 6553Any2, 7563Any3, 8573Any1, 4, 7583Any2, 5, 8593Any3, 6, 960N/AN/AN/A61N/AN/AN/A62N/AN/AN/A633Even9
TABLE 3Random access configuration of the LTE TDD systemPRACHDensityConfigurationPreamblePer 10 msVersionIndexFormat(DRA)(rRA)000.50100.51200.523010401150126020702180229030100311103212040130411404215050160511705218060190612010.502110.512210.52231102411125120261302714028150291603020.503120.513220.52332103421135220362303724038250392604030.504130.514230.5243310443114532046330473404840.504940.515040.5251410524115342054430554405645057460
Referring again to FIG. 1, the random access response in operation 110 includes timing advance information. The terminal transmits the message in operation 115 based on the timing advance information. According to LTE standards, a mobile terminal may enter the asynchronous state when the mobile terminal enters an IDLE state or the mobile terminal does not receive timing advance signaling over a long period of time. When the terminal in the asynchronous state finds that there is uplink data needed to be transmitted, the terminal may complete the entire random access procedure to enter an uplink synchronization state. As mentioned earlier, a feature of a terminal in the Internet of Things is a small data amount, a long duty cycle with sporadic transmission, and a large number of access devices. The long duty cycle means that when the terminal completes data transmission, the terminal may enter a sleep state to reduce energy consumption. This means that the terminal loses the uplink synchronization and must perform the random access procedure again during the next data transmission. Under the circumstance of a small data amount and a large number of access devices, such frequent random access procedure becomes very inefficient. Such inefficiency is reflected in that a great deal of overhead is used to perform the random access procedure, while the data transmission supported by the overhead is extremely small.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.